Dr. Rob Veis

Anterior cross-bites are one of the most common orthodontic problems in growing children. They usually occur in the primary and mixed dentition as a result of disharmony in either the skeletal, functional or dental components of the orthognathic system of the child. Some of the more common etiologic factors are trauma to the primary incisors with displacement of the permanent tooth bud; delayed exfoliation of the primary incisor with palatal deflection of the erupting permanent incisor; supernumerary anterior teeth; odontomas; congenitally abnormal eruption patterns and arch perimeter deficiencies.

Types of Anterior Cross-Bites

1. Patients who have a simple anterior dental cross-bite exhibit the following characteristics:

• The cross-bite usually involves only one or two teeth.
• The facial profile is normal in centric relation and centric occlusion.
• The anterior posterior skeletal relationship is normal.
• The mandible has a smooth arc of closure into an Angle Class I molar and cuspid relationship, with a coincident centric relation and centric occlusion.
• A disharmony in the dental components results from an abnormal axial inclination of either the maxillary or mandibular anterior teeth as they erupt. This can be cephalometrically verified by looking at the upper incisor to NB angle. The rest of the teeth are usually in a normal scheme.

2. Patients who have a functional anterior cross-bite (Pseudo Class III) exhibit the following characteristics:

• In centric relation or in a relaxed postural position, the patient presents with a normal facial profile convexity.
• In centric relation, the opposing incisors generally contact edge to edge with the molars separated but in an Angle Class I relation.
• During closing, an early occlusal interference causes an anterior shift of the mandible.
• As the mandible shifts forward into centric occlusion, the incisors are placed into cross-bite and the molars into a Class III relationship.
• Depending on the severity of the anterior shift when the patient closes into centric occlusion, they will either maintain a straight profile or exhibit a concave facial profile.
• The maxillary incisors are generally retroclined and the mandibular incisors may be proclined.
• In a pseudo Class III, the gonial angle is more nearly a right angle with the average near 120 degrees. In addition, a false normal ANB angle may be manifested in a pseudo Class III.

3. Patients who have a true skeletal Class III or mesioocclusion have a problem of skeletal dysplasia involving mandibular hypertrophy, a marked shortening of the cranial base or maxilla, or a combination of both. Some of the characteristics they will exhibit are:

• In centric relation, their facial profile will be straight or concave.
• In centric relation, there will be a Class III molar relationship and an anterior cross-bite.
• In centric occlusion, there will be a Class III molar relationship and an anterior cross-bite.
• The arc of mandibular closure remains smooth without any occlusal interferences.
• In an attempt to compensate for the skeletal discrepancy during growth, the maxillary incisors usually become proclined and the mandibular incisors become retroclined.
• Cephalometrically, a reduced or negative value for the ANB angle indicates that either the maxilla is relatively retracted or the mandible is positioned anteriorly. If the SNA angle value decreases beyond the standard deviation for the age and sex of the child, and the SNB angle is normal, the dentist should consider fault in the maxillary dental component. If the SNB angle value decreases over the standard deviation for the age and sex of the child, then the dentist should consider fault in the mandibular skeletal component.
• Another cephalometric characteristic found in a skeletal Class III is that the gonial angle is more often obtuse with a range between 130 and 140 degrees (this gives a long facial appearance). It should also be noted that a high SN to Mandibular Plane Angle can mask a developing Class III malocclusion. An in-depth cephalometric analysis is a must before treating these cases.

Treatment Overview

The anterior cross-bite must be treated in the primary and mixed dentition. Allowing this malocclusion to continue into the permanent dentition without correction will result in a reduction of treatment options and provide a less than ideal environment for growth to proceed in an orderly fashion. Specifically, the anterior cross-bite can lead to the following problems which, when left untreated, will require more extensive orthodontic therapy at a later time: labial displacement of the opposing mandibular incisor; gingival inflammation and recession of the investing tissues surrounding the mal-opposed teeth; occlusal trauma, enamel abrasion or fractures of the anterior teeth; the development of abnormal chewing and swallowing problems; abnormal growth of the maxilla and the mandible; the development of a permanent Class III dentofacial abnormality and temporomandibular joint dysfunction.

1. The best treatment of a simple dental cross-bite is to prevent the condition from ever happening. This can be accomplished by taking routine radiographic images of the maxillary incisor region to look for abnormalities like an odontoma, the delayed exfoliation of a primary incisor or the presence of a supernumerary tooth. Observing and managing severe arch perimeter deficiency is also essential to prevent a cross-bite from occurring.
   
   If a dental anterior cross-bite exists, methods to correct it range from the use of an acrylic incline plane to a reverse stainless steel crown. Even tongue-blades have been used to try to jump a cross-bite. The key to success is to use an appliance that is both comfortable and predictable such as a simple Hawley retainer with recurve springs or a fixed labial-lingual appliance (including a vertical removable arch for ease of adjustment with a recurve spring to jump the cross-bite). Both of these appliances work by tipping the maxillary teeth forward so they are in a normal dental relationship to the mandibular teeth. Once this is accomplished, it will allow future coordinated growth between the maxilla and the mandible.
   
2. Treatment of a functional anterior cross-bite should be undertaken as soon as possible to eliminate the mandibular shift that takes place (shift subjects incisors to abnormal occlusal interferences and, over time, the forward positioning of the mandible may alter the patient's growth resulting in a skeletal Class III pattern). Once a functional cross-bite exists, correction can be obtained with an Upper Anterior Cross-Bite Appliance. The entire anterior segment can be moved labially with an expansion screw placed 90 degrees to the maxillary incisors. A labial arch wire moves with the segment as a unit while using the posterior teeth for anchorage and retention. A posterior bite plane is necessary if the anterior teeth are locked behind the lower incisors.
   
3. There is no simple orthodontic correction for a skeletal anterior cross-bite. In the hands of the orthodontist, the first step is to do a differential diagnosis of the location of the skeletal problem. Early treatment of the Class III involving mandibular excess is generally avoided. The treatment of choice for this skeletal problem is comprehensive orthodontics and/or orthognathic surgery when growth is complete. For patients presenting with a retruded maxilla, early orthopedic treatment using a fixed rapid palatal expansion appliance with a protraction headgear is possible (most effective in early mixed dentition cases).